For example, the Enterprise Gantt Chart uses the Enterprise Entry table and both are contained by default in the enterprise ...

For example, the  Enterprise Gantt Chart uses the Enterprise Entry table and both are contained by default in the enterprise global template. If you are working in a project where the Enterprise Gantt Chart and Enterprise Entry table are active and you attempt to insert a new column, this error message will appear. If you close the project, your formatting change (the new column) will be lost because the  Enterprise Entry table from the enterprise global template is reapplied.